Bulk Heating a Subsurface Formation

ABSTRACT

Systems and methods for bulk heating of a subsurface formation with at least a pair of electrode assemblies in the subsurface formation are disclosed. The method may include electrically powering the pair of electrode assemblies to resistively heat a subsurface region between the pair of electrode assemblies with electrical current flowing through the subsurface region between the pair of electrode assemblies; flowing a shunt mitigator into at least one of the pair of electrode assemblies; and mitigating a subsurface shunt between the pair of electrode assemblies with the shunt mitigator. Mitigating may be responsive to a shunt indicator that indicates a presence of the subsurface shunt.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication 62/087,655 filed Dec. 4, 2014 entitled BULK HEATING ASUBSURFACE FORMATION, the entirety of which is incorporated by referenceherein.

FIELD

The present disclosure relates to systems and methods for bulk heating asubsurface formation. More specifically, the present disclosure relatesto systems and methods for mitigating subsurface shunts during bulkheating of a subsurface formation.

BACKGROUND

Certain subsurface formations may include organic matter, such as shaleoil, bitumen, and/or kerogen, which has material and chemical propertiesthat may complicate production of fluid hydrocarbons from the subsurfaceformation. For example, the organic matter may not flow at a ratesufficient for production. Moreover, the organic matter may not includesufficient quantities of desired chemical compositions (typicallysmaller hydrocarbons). Hence, recovery of useful hydrocarbons from suchsubsurface formations may be uneconomical or impractical.

Heating of organic matter-containing subsurface formations may beparticularly useful to generate producible hydrocarbons from immatureorganic-rich source rocks in situ. For example, heating organicmatter-containing subsurface formations may pyrolyze kerogen into mobileliquids and gases, and may reduce the viscosity of heavy oil to enhancehydrocarbon mobility.

One method to heat a subsurface formation is to conduct electricitythrough the formation and, thus, resistively heat the subsurfaceformation. This method of heating a subsurface formation may be referredto as “bulk heating” or “volumetric heating” of the subsurfaceformation. Bulk heating of the subsurface formation may be accomplishedby conducting electricity between electrode assemblies in the subsurfaceformation and through a subsurface region (volume) of naturallyelectrically-resistive rock between the electrode assemblies. Theelectrode assemblies may be contained in wellbores and/or manmadefractures, and the electrode assemblies may include electricalconductors, such as metal rods and/or granular electrically conductivematerials. Bulk heating may include applying a voltage gradient acrossthe subsurface region to initiate a relatively uniform electricalcurrent flow through the subsurface region. Heat may be generated withinthe volume of the subsurface region due to electrical resistive lossresulting from the current flow through the volume of the subsurfaceregion (Joule heating). Bulk heating performance may not be dependent onapplied thermal gradients or rock thermal conductivity—physicalconstraints that can impede feasibility of subsurface formation heatingschemes based on thermal conduction.

As heating occurs in subsurface regions between the pairs of electrodeassemblies, the electrical conductivity (or alternatively, resistivity)of the subsurface regions may change. This change in the electricalconductivity (or resistivity) of the subsurface regions may be due tophysical and/or chemical changes within the subsurface regions, forexample, due to temperature sensitivity of the electrical resistance ofthe native rock, due to native brine boiling off, due to disassociationand boil off of chemically bound water, and/or due to pyrolysis (and/orcoking) of native hydrocarbons.

Heating a subsurface region via electrical conduction through thesubsurface region may not occur uniformly and may suffer frominstabilities, in particular if conductivity within the subsurfaceregion increases strongly with increasing temperature. The conductivityincrease within the subsurface region may result from pyrolysisoccurring and may lead to the formation of electrically conductive cokeor other graphitic materials. When electrical conductivity increasesstrongly with increasing temperature, hotter regions will become evenhotter, since electricity may channel through the hotter (and moreconductive) regions. Ultimately, this positive correlation betweentemperature and electrical conductivity may lead to the formation of anarrow, highly conductive shunt (also called a channel) between theelectrode assemblies that will short-circuit the electrical flow betweenthe electrode assemblies. Although the electrode assemblies may be largein extent or area, the bulk of the electrical flow may occur through avery small zone, and heating of the subsurface region between theelectrode assemblies may be quite uneven. This phenomenon is analogousto viscous fingering that may occur when a low viscosity fluid is driventhrough a higher viscosity fluid. In bulk heating, the tendency forshunting instabilities to occur and the rate of shunt growth may bedependent on the heating rate and the extent to which electrical andphysical property heterogeneities exist within the subsurface regions.

Conventional methods to minimize the effects of subsurface shunts duringbulk heating include disconnecting at least one of the affectedelectrode assemblies (electrode assemblies that conduct current into ashunted region). Disconnecting the affected electrode assembly stops thegeneration of heat in the shunted region, and any other (unaffected)subsurface regions, served by the affected electrode.

In view of the aforementioned disadvantages, there is a need foralternative methods and systems for bulk heating a subsurface formation.More specifically, there is a need for alternative methods and systemsfor mitigating the effects of subsurface shunts during bulk heating of asubsurface formation.

SUMMARY

It is an object of the present disclosure to provide systems and methodsfor bulk heating of a subsurface formation. More specifically, it is anobject of the present disclosure to provide systems and methods formitigating effects of subsurface shunts during bulk heating of asubsurface formation.

A method for bulk heating a subsurface formation with at least a pair ofelectrode assemblies in the subsurface formation may includeelectrically powering the pair of electrode assemblies to resistivelyheat a subsurface region between the pair of electrode assemblies withelectrical current flowing through the subsurface region between thepair of electrode assemblies; flowing a shunt mitigator into at leastone of the pair of electrode assemblies; and, responsive to a shuntindicator, mitigating a subsurface shunt between the pair of electrodeassemblies with the shunt mitigator, wherein the shunt indicatorindicates a presence of the subsurface shunt.

A method for bulk heating a subsurface formation with at least a pair ofelectrode assemblies in the subsurface formation may includeelectrically powering the pair of electrode assemblies to resistivelyheat an in situ resistive heater, wherein the in situ resistive heateris a subsurface region of the subsurface formation between the pair ofelectrode assemblies; upon determining a presence of a subsurface shuntbetween the pair of electrode assemblies, forming a modified in situresistive heater by mitigating the subsurface shunt; and electricallypowering the pair of electrode assemblies to resistively heat themodified in situ resistive heater.

A subsurface formation may include at least a pair of electrodeassemblies, wherein each electrode assembly of the pair of electrodeassemblies may include an electrically conductive material, and whereinat least one electrode assembly of the pair of electrode assemblies mayinclude a shunt mitigator that is selected to undergo a state change inresponse to a shunt indicator.

The foregoing has broadly outlined the features of the presentdisclosure so that the detailed description that follows may be betterunderstood. Additional features will also be described herein.

DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the presentdisclosure will become apparent from the following description and theaccompanying drawings, which are briefly discussed below.

FIG. 1 is a schematic representation of electrode assemblies in asubsurface formation.

FIG. 2 is a schematic representation of bulk heating methods to mitigatesubsurface shunt formation.

FIG. 3 is a schematic representation of the system of FIG. 1 during theapplication of a shunt mitigator.

FIG. 4 is a schematic representation of the system of FIG. 3 after thesubsurface shunt is mitigated.

FIG. 5 is a schematic representation of bulk heating methods that areresponsive to subsurface shunt formation.

It should be noted that the figures are merely examples and nolimitations on the scope of the present disclosure are intended thereby.Further, the figures are generally not drawn to scale, but are draftedfor purposes of convenience and clarity in illustrating various aspectsof the disclosure.

DETAILED DESCRIPTION

For the purpose of promoting an understanding of the principles of thedisclosure, reference will now be made to the features illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of thedisclosure is thereby intended. Any alterations and furthermodifications, and any further applications of the principles of thedisclosure as described herein, are contemplated as would normally occurto one skilled in the art to which the disclosure relates. It will beapparent to those skilled in the relevant art that some features thatare not relevant to the present disclosure may not be shown in thedrawings for the sake of clarity.

At the outset, for ease of reference, certain terms used in thisapplication and their meanings as used in this context are set forthbelow. To the extent a term used herein is not defined below, it shouldbe given the broadest definition persons in the pertinent art have giventhat term as reflected in at least one printed publication or issuedpatent. Further, the present processes are not limited by the usage ofthe terms shown below, as all equivalents, synonyms, new developmentsand terms or processes that serve the same or a similar purpose areconsidered to be within the scope of the present disclosure.

As used herein, the term “hydrocarbon” refers to an organic compoundthat includes primarily, if not exclusively, the elements hydrogen andcarbon. Hydrocarbons may also include other elements, such as, but notlimited to, halogens, metallic elements, nitrogen, oxygen, and/orsulfur. Hydrocarbons generally fall into two classes: aliphatic, orstraight chain hydrocarbons, and cyclic, or closed ring hydrocarbons,including cyclic terpenes. Examples of hydrocarbon-containing materialsinclude any form of natural gas, oil, coal, heavy oil and kerogen thatcan be used as a fuel or upgraded into a fuel.

“Heavy oil” includes oils which are classified by the American PetroleumInstitute (“API”), as heavy oils, extra heavy oils, or bitumens. Theterm “heavy oil” includes bitumen. Heavy oil may have a viscosity ofabout 1,000 centipoise (cP) or more, 10,000 cP or more, 100,000 cP ormore, or 1,000,000 cP or more. In general, a heavy oil has an APIgravity between 22.3° API (density of 920 kilograms per meter cubed(kg/m³) or 0.920 grams per centimeter cubed (g/cm³)) and 10.0° API(density of 1,000 kg/m³ or 1 g/cm³). An extra heavy oil, in general, hasan API gravity of less than 10.0° API (density greater than 1,000 kg/m³or 1 g/cm³). For example, a source of heavy oil includes oil sand orbituminous sand, which is a combination of clay, sand, water andbitumen. The recovery of heavy oils is based on the viscosity decreaseof fluids with increasing temperature or solvent concentration. Once theviscosity is reduced, the mobilization of fluid by steam, hot waterflooding, or gravity is possible. The reduced viscosity makes thedrainage or dissolution quicker and therefore directly contributes tothe recovery rate.

As used herein, the term “fluid” refers to gases, liquids, andcombinations of gases and liquids, as well as to combinations of gasesand solids, and combinations of liquids and solids.

As used herein, the term “formation hydrocarbons” refers to both lightand/or heavy hydrocarbons and solid hydrocarbons that are contained inan organic-rich rock formation. Formation hydrocarbons may be, but arenot limited to, natural gas, oil, kerogen, oil shale, coal, tar, naturalmineral waxes, and asphaltenes.

As used herein, the term “gas” refers to a fluid that is in its vaporphase at 1 atmosphere (atm) and 15 degrees Celsius (° C.).

As used herein, the term “kerogen” refers to a solid, insolublehydrocarbon that may principally contain carbon, hydrogen, nitrogen,oxygen, and/or sulfur.

As used herein, the term “oil” refers to a hydrocarbon fluid containingprimarily a mixture of condensable hydrocarbons.

As used herein, the term “oil shale” refers to any fine-grained,compact, sedimentary rock containing organic matter made up mostly ofkerogen, a high-molecular weight solid or semi-solid substance that isinsoluble in petroleum solvents and is essentially immobile in its rockmatrix.

As used herein, the term “organic-rich rock” refers to any rock matrixholding solid hydrocarbons and/or heavy hydrocarbons. Rock matrices mayinclude, but are not limited to, sedimentary rocks, shales, siltstones,sands, silicilytes, carbonates, and diatomites. Organic-rich rock maycontain kerogen.

As used herein, the term “organic-rich rock formation” refers to anyformation containing organic-rich rock. Organic-rich rock formationsinclude, for example, oil shale formations, coal formations, oil sandsformations or other formation hydrocarbons.

As used herein, “overburden” refers to the material overlying asubsurface (subterranean) reservoir. The overburden may include rock,soil, sandstone, shale, mudstone, carbonate and/or ecosystem above thesubsurface reservoir. During surface mining, the overburden is removedprior to the start of mining operations. The overburden may refer toformations above or below free water level. The overburden may includezones that are water saturated, such as fresh or saline aquifers. Theoverburden may include zones that are hydrocarbon bearing.

As used herein, the term “pyrolysis” refers to the breaking of chemicalbonds through the application of heat. For example, pyrolysis mayinclude transforming a compound into one or more other substances byheat alone or by heat in combination with an oxidant. Pyrolysis mayinclude modifying the nature of the compound by addition of hydrogenatoms which may be obtained from molecular hydrogen, water, carbondioxide, or carbon monoxide. Heat may be transferred to a section of theformation to cause pyrolysis.

As used herein, “reservoir,” “subsurface reservoir,” or “subterraneanreservoir” is a subsurface rock or sand formation from which aproduction fluid or resource can be harvested. The rock formation mayinclude sand, granite, silica, carbonates, clays, and organic matter,such as oil shale, light or heavy oil, gas, or coal, among others.Reservoirs can vary in thickness from less than one foot (0.3048 meter(m)) to hundreds of feet (hundreds of meters).

As used herein, the term “solid hydrocarbons” refers to any hydrocarbonmaterial that is found naturally in substantially solid form atformation conditions. Non-limiting examples include kerogen, coal,shungites, asphaltites, and natural mineral waxes.

As used herein “subsurface formation” refers to the material existingbelow the Earth's surface. The subsurface formation may interchangeablybe referred to as a formation or a subterranean formation. Thesubsurface formation may comprise a range of components, e.g. mineralssuch as quartz, siliceous materials such as sand and clays, as well asthe oil and/or gas that is extracted.

As used herein, “underburden” refers to the material underlaying asubterranean reservoir. The underburden may include rock, soil,sandstone, shale, mudstone, wet/tight carbonate and/or ecosystem belowthe subterranean reservoir.

As used herein, “wellbore” is a hole in the subsurface formation made bydrilling or inserting a conduit into the subsurface. A wellbore may havea substantially circular cross section or any other cross-section shape,such as an oval, a square, a rectangle, a triangle, or other regular orirregular shapes. The term “well,” when referring to an opening in theformation, may be used interchangeably with the term “wellbore.”Further, multiple pipes may be inserted into a single wellbore, forexample, as a liner configured to allow flow from an outer chamber to aninner chamber.

The terms “approximately,” “about,” “substantially,” and similar termsare intended to have a broad meaning in harmony with the common andaccepted usage by those of ordinary skill in the art to which thesubject matter of this disclosure pertains. It should be understood bythose of skill in the art who review this disclosure that these termsare intended to allow a description of certain features described andclaimed without restricting the scope of these features to the precisenumeral ranges provided. Accordingly, these terms should be interpretedas indicating that insubstantial or inconsequential modifications oralterations of the subject matter described and are considered to bewithin the scope of the disclosure.

The articles “the”, “a” and “an” are not necessarily limited to meanonly one, but rather are inclusive and open ended so as to include,optionally, multiple such elements.

“At least one,” in reference to a list of one or more entities should beunderstood to mean at least one entity selected from any one or more ofthe entity in the list of entities, but not necessarily including atleast one of each and every entity specifically listed within the listof entities and not excluding any combinations of entities in the listof entities. This definition also allows that entities may optionally bepresent other than the entities specifically identified within the listof entities to which the phrase “at least one” refers, whether relatedor unrelated to those entities specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) mayrefer, to at least one, optionally including more than one, A, with no Bpresent (and optionally including entities other than B); to at leastone, optionally including more than one, B, with no A present (andoptionally including entities other than A); to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other entities). In other words,the phrases “at least one,” “one or more,” and “and/or” are open-endedexpressions that are both conjunctive and disjunctive in operation. Forexample, each of the expressions “at least one of A, B and C,” “at leastone of A, B, or C,” “one or more of A, B, and C,” “one or more of A, B,or C” and “A, B, and/or C” may mean A alone, B alone, C alone, A and Btogether, A and C together, B and C together, A, B and C together, andoptionally any of the above in combination with at least one otherentity.

Where two or more ranges are used, such as but not limited to 1 to 5 or2 to 4, any number between or inclusive of these ranges is implied.

As used herein, the phrase, “for example,” the phrase, “as an example,”and/or simply the term “example,” when used with reference to one ormore components, features, details, structures, and/or methods accordingto the present disclosure, are intended to convey that the describedcomponent, feature, detail, structure, and/or method is an illustrative,non-exclusive example of components, features, details, structures,and/or methods according to the present disclosure. Thus, the describedcomponent, feature, detail, structure, and/or method is not intended tobe limiting, required, or exclusive/exhaustive; and other components,features, details, structures, and/or methods, including structurallyand/or functionally similar and/or equivalent components, features,details, structures, and/or methods, are also within the scope of thepresent disclosure.

As used herein, the terms “adapted” and “configured” mean that theelement, component, or other subject matter is designed and/or intendedto perform a given function. Thus, the use of the terms “adapted” and“configured” should not be construed to mean that a given element,component, or other subject matter is simply “capable of” performing agiven function but that the element, component, and/or other subjectmatter is specifically selected, created, implemented, utilized,programmed, and/or designed for the purpose of performing the function.It is also within the scope of the present disclosure that elements,components, and/or other recited subject matter that is recited as beingadapted to perform a particular function may additionally oralternatively be described as being configured to perform that function,and vice versa. Similarly, subject matter that is recited as beingconfigured to perform a particular function may additionally oralternatively be described as being operative to perform that function.

FIGS. 1-5 provide examples of systems and methods for bulk heating of asubsurface formation. More specifically, FIGS. 1-5 provide examples ofsystems and methods for mitigating subsurface shunts during bulk heatingof a subsurface formation. Elements that serve a similar, or at leastsubstantially similar, purpose are labeled with numbers consistent amongthe figures. The corresponding elements with like numbers in each of thefigures may not be discussed in detail herein with reference to each ofthe figures. Similarly, all elements may not be labeled in each of thefigures, but associated reference numerals may be utilized forconsistency. Elements, components, and/or features that are discussedwith reference to one or more of the figures may be included in and/orutilized with any of the figures without departing from the scope of thepresent disclosure.

In general, elements that are likely to be included are illustrated insolid lines, while elements that are optional are illustrated in dashedlines. However, elements that are shown in solid lines may not beessential. Thus, an element shown in solid lines may be omitted withoutdeparting from the scope of the present disclosure.

FIG. 1 is a schematic representation of a bulk heating system 10. Bulkheating systems 10 may include at least two electrode assemblies 50 thatextend into a subsurface formation 20. The at least two electrodeassemblies 50 may form, or define, at least a pair of electrodeassemblies 50. More specifically, electrode assemblies 50 are inelectrical communication with a subsurface formation 20, and theelectrode assemblies are configured in adjacent pairs to form electricalcircuits with a subsurface region 32 between each pair of electrodeassemblies 50. Individual electrode assemblies 50 may be a member ofmore than one pair of electrode assemblies 50 and may be in electricalcommunication with more than one subsurface region 32. For clarity, FIG.1 illustrates in solid lines two spaced-apart electrode assemblies 50.As schematically illustrated with dashed lines, bulk heating systems 10may include more than two electrode assemblies 50, for example, 3, 4, 5,6, or more than 6 electrode assemblies 50.

Subsurface formation 20 is a finite subsurface (subterranean) region.Subsurface formation 20 may be of any geologic form and may contain oneor more organic matter-containing regions (e.g., layers, intervals,etc.), one or more regions with little to no organic matter, anoverburden, and/or an underburden. Subsurface formation 20 may be belowan overburden and/or above an underburden. In FIG. 1, subsurfaceformation 20 is schematically indicated to include organic matter 30(e.g., a solid, liquid, and/or gaseous hydrocarbon mineral such ashydrocarbon compounds, shale oil, bitumen, bituminous coal, and/orkerogen). Subsurface formation 20 may be at least 100 m, at least 200 m,at least 500 m, at least 1,000 m, at least 2,000 m, at least 5,000 m, atmost 20,000 m, at most 10,000 m, at most 5,000 m, at most 2,000 m, atmost 1,000 m, and/or at most 500 m below the Earth's surface 22.Suitable depth ranges may include combinations of any upper and lowerdepth listed above or any number within or bounded by the precedingdepth ranges.

Subsurface regions 32 may be portions of the subsurface formation 20that are in electrical contact with at least two electrode assemblies50, i.e., subsurface regions 32 adjoin at least two adjacent electrodeassemblies 50. Subsurface regions 32 generally may extend between atleast a pair of electrode assemblies 50.

Subsurface regions 32 may be the regions of subsurface formation 20 thatare heated by the bulk heating system 10 via electrical resistiveheating (Joule heating). Subsurface regions 32 may be electricallypowered (also called energized) to cause resistive heating, i.e.,electrical power dissipated within a given subsurface region 32 may heatthe given subsurface region 32. Electrically powering (also referred toas transmitting electricity) may be the result of connecting differentvoltages to different electrode assemblies 50 and applying the voltagesto cause current to flow through the subsurface region 32 between theelectrode assemblies 50. When electrically powered and resistivelyheating, subsurface regions 32 may be referred to as in situ resistiveheaters 34. The heating and/or the power dissipated within thesubsurface regions 32 may be expressed as power deposited and/ordissipated per volume (or length cubed). For illustration purposes, insitu resistive heaters 34 are depicted schematically via exampleelectrical flow lines between adjacent electrode assemblies 50. Itshould be understood that electricity flow is occurring over the entireexposed surface of an electrode assembly 50 and not just where flowlines are shown.

Electrode assemblies 50 may include at least one wellbore 40 and/orfracture 44. Electrode assemblies 50 may include electrically conductivematerial sufficient to conduct electricity from the surface 22 to theadjoining subsurface region(s) 32 without undue power loss (due toelectrical resistive heating). An electrode assembly 50 may beelectrically connected to one or more subsurface regions 32 of thesubsurface formation 20 that adjoin the electrode assembly 50. Anelectrode assembly 50 may include a wellbore 40 that includes anelectrically conductive wire, cable, casing, tubular, rod, etc., andthat is electrically connected to at least one subsurface region 32adjoining the wellbore 40. An electrode assembly 50 may include afracture 44 that includes conductive media, such as electricallyconductive particulate and/or electrically conductive fluid.

Wellbores 40 may be substantially vertical, substantially horizontal,any angle between vertical and horizontal, deviated or non-deviated, andcombinations thereof, for example, a vertical well with a non-verticalsegment. As used herein, “substantially vertical” means within 15° oftrue vertical and “substantially horizontal” means within 15° of truehorizontal. Wellbores 40 may include and/or may be supported, lined,sealed, and/or filled with materials such as casings, linings, sheaths,conduits, electrically conductive materials (e.g., metal rods, metalcables, metal wires, metal tubulars, electrically conductiveparticulate, electrically conductive granular materials, and/orelectrically conductive liquid). Wellbores 40 may be configured to be inelectrical and/or fluidic communication with the subsurface formation 20and/or one or more subsurface regions 32.

Fractures 44 may be natural and/or manmade cracks, or surfaces ofbreakages, within rock in the subsurface formation 20. Fractures 44 maybe induced mechanically in subsurface regions, for example, by hydraulicfracturing (in which case, the fracture 44 may be referred to as ahydraulic fracture). Another example of a method of forming of fractures44 is steam fracturing (in which case, the fracture 44 may be referredto as a steam fracture). Fractures 44 may be referred to as hydraulicfractures and steam fractures, respectively. Fractures 44 may besubstantially planar. Fractures 44 may be substantially vertical,substantially horizontal, any angle between vertical and horizontal,branched, networked, and combinations thereof, for example, a planarvertical fracture with a non-vertical branch. The length of a fracture44 may be a distance from the source of the fracture (e.g., a wellbore40 used to establish the fracture) to a fracture tip (the furthest pointof the fracture from the source) or the distance along the fracturebetween the two farthest spaced fracture tips. Fractures 44 may beconfigured to be in electrical and/or fluidic communication with thesubsurface formation 20 and/or one or more subsurface regions 32. Forillustration purposes, the widths of the fractures 44 are exaggeratedcompared to the length of the fractures. For example, fracture widthsmay be on order of a few millimeters or centimeters, whereas fracturelengths may be on order of tens or hundreds of meters.

Fractures 44 may be held open with granular material called proppant.Fractures 44 may include and/or may be supported, lined, sealed, and/orfilled with other materials, such as electrically conductive materials,particulate, granular materials, liquids, and/or gases. Proppant may beelectrically conductive. Electrically conductive materials may includeat least one of granular material, granules, particles, filaments,metal, granular metal, metal coated particles, coke, graphite,electrically conductive gel, and electrically conductive liquid. Forexample, the proppant may include, and/or may be, graphite particles. Asother examples, the proppant may include, and/or may be, an electricallyconductive material, such as metal particles, metal coated particles,and/or coke particles.

Electrode assemblies 50 may be arranged in pairs of adjacent electrodeassemblies 50 within the subsurface formation. The pair of electrodeassemblies 50 in each pair of adjacent electrode assemblies 50 may benearer to each other than to other, non-adjacent electrode assemblies50. Relative to a given electrode assembly 50, an adjacent electrodeassembly 50 may be the closest electrode assembly 50 or one of theclosest electrode assemblies 50. Pairs of adjacent electrode assemblies50 are not necessarily within a small distance of each other and may beseparated by distances of hundreds of meters. The distance betweenelectrode assemblies 50 is the shortest distance between the electrodeassemblies 50 through the subsurface region 32 that separates theelectrode assemblies 50. Electrode assemblies 50 may be deemed adjacentwhen no other electrode assembly 50 intersects a line spanning theshortest distance between the electrode assemblies 50.

Electrode assemblies 50 may be arranged in pairs, groups, rows, columns,and/or arrays. The electrode assemblies 50 may be spaced apart and mayhave a substantially uniform spacing (at least in one direction). Forexample, electrode assemblies may be spaced apart with a spacing of atleast 5 m, at least 10 m, at least 20 m, at least 50 m, at least 100 m,at least 200 m, at most 500 m, at most 200 m, at most 100 m, at most 50m, and/or at most 20 m. Groups, rows, columns, and arrays of electrodeassemblies 50 may include inside electrode assemblies 52 and outerelectrode assemblies 54. Outer electrode assemblies 54 may be adjacentand/or connected to fewer electrode assemblies 50 than inside electrodeassemblies 52. For example, rows and columns of electrode assemblies 50may include a first outer electrode assembly 54 at one end of the row orcolumn and a second outer electrode assembly 54 at the other end of therow or column. The first outer electrode assembly 54 may be adjacent toonly one electrode assembly 50; the second outer electrode assembly 54may be adjacent to only one electrode assembly 50; and the insideelectrode assemblies 52 may each be adjacent to two electrode assemblies50 of the electrode assemblies in the row or column. The insideelectrode assemblies 52 may be referred to as middle electrodeassemblies 52, central electrode assemblies 52, intermediate electrodeassemblies 52, inner electrode assemblies 52, and/or interior electrodeassemblies 52. The outer electrode assemblies 54 may be referred to asedge electrode assemblies 54 and/or end electrode assemblies 54.

Electrode assemblies 50 may be oriented with respect to each other. Forexample, two or more electrode assemblies 50 (or portions thereof) maybe at least substantially parallel to each other and substantiallyfacing each other. In particular, two electrode assemblies 50 may eachinclude a generally planar fracture 44, and the fractures 44 of theelectrode assemblies 50 may be substantially parallel to each other,with each electrode assembly 50 including a face, or generally planarfracture surface, 46 that faces a corresponding face 46 of the otherelectrode assembly 50. In the example of FIG. 1, two substantiallyparallel fractures 44 (shown in solid lines) each form a portion of twoseparate electrode assemblies 50. The two solid-line electrodeassemblies 50 illustrated in FIG. 1 may be deemed parallel electrodeassemblies 50.

Adjacent electrode assemblies 50 may be configured to transmitelectricity and/or to electrically power the subsurface region(s) 32between the adjacent electrode assemblies 50. The electrode assemblies50 may be configured to apply a voltage across and/or to supply anelectrical current through the corresponding subsurface region(s) 32.Electrical power supplied to the subsurface region(s) 32 may be DC(direct current) power and/or AC (alternating current) power. Theelectrical power may be supplied by an electrical power source 70. Asindicated in FIG. 1, electrical power source 70 may be electricallyconnected to the electrode assemblies 50 from a surface (above-ground)location 22. DC power may be supplied by applying a voltage difference(gradient) across the subsurface region 32. In a DC poweredconfiguration, one of the electrode assemblies 50 contacting thesubsurface region 32 may have a higher voltage (called the high voltageand/or the high polarity), and another electrode assembly 50 contactingthe subsurface region 32 may have a lower voltage (called the lowvoltage and/or the low polarity). If the high polarity is a positivevoltage and the low polarity is a negative voltage, the high polarityand the low polarity may be referred to as the positive polarity and thenegative polarity, respectively. Where DC power is supplied, thevoltages of the electrode assemblies 50 may be occasionally (e.g.,periodically) switched, for example, to avoid electrochemical effectsand electrode degradation at the electrode assemblies 50.

AC power may be supplied by applying different voltage waveforms (alsocalled alternating voltages) to different electrode assemblies 50 incontact with the same subsurface region 32. Generally, the appliedalternating voltages are periodic, have the same frequency, and havediffering phase angles. Suitable AC frequencies include at least 10 Hz(hertz), at least 30 Hz, about 50 Hz, about 60 Hz, about 100 Hz, about120 Hz, at least 100 Hz, at least 200 Hz, at least 1,000 Hz, at least10,000 Hz, at most 100,000 Hz, at most 300,000 Hz, at most 1,000,000 Hz,at most 5,000,000 Hz, and/or at most 15,000,000 Hz. Suitable ranges mayinclude combinations of any upper and lower AC frequency listed above orany number within or bounded by the AC frequencies listed above. The ACfrequency may be selected to be below a frequency at whichradio-frequency (dielectric) heating dominates over resistive (Joule)heating of the subsurface formation 20.

AC power may be supplied as one or more alternating voltages, and eachelectrode assembly 50 may have an alternating voltage or a DC voltageapplied. For example, AC power may be supplied in a single-phaseconfiguration where an alternating voltage is applied to one electrodeassembly 50 and a DC voltage (also referred to as a neutral voltage) isapplied to another electrode assembly 50. As other examples, AC powermay be supplied in a two-phase configuration, a three-phaseconfiguration, and/or in a multi-phase configuration. The ‘electricalphases’ available in a multi-phase configuration are alternatingvoltages having the same frequency and different phase angles (i.e.,nonequal phase angles). Generally, the phase angles are relativelyevenly distributed within the period of the AC power (the period is theinverse of the shared frequency of the alternating voltages). Forexample, common phase angles for a two-phase configuration are 0° and180° (a phase angle difference of ±180°, i.e., of 180° in absolutevalue), and 0° and 120° (for example, two of the three poles from a3-phase generator). Common phase angles for a three-phase configurationare 0°, 120°, and 240° (phase angle differences of ±120°, i.e., of 120°in absolute value). Though less common, other multi-phase configurations(e.g., 4, 5, 6, or more ‘electrical phases’) and/or other phase angles,and other phase angle differences, may be utilized to supply AC power.

When electrical power is supplied to subsurface regions 32, thesubsurface regions 32 may resistively heat and become more electricallyconductive. As the subsurface regions 32 are heated, the electricalconductivity may increase (and the electrical resistivity may decrease)due to physical and/or chemical changes within the subsurface regions32, for example, due to temperature sensitivity of the electricalresistance of the native rock, due to native brine boiling off, and/ordue to pyrolysis (and/or coking) of native organic matter and/or nativehydrocarbons. Before heating, the subsurface regions 32 may berelatively poorly electrically conductive, for example, having anaverage electrical conductivity of less than 1 S/m (Siemens/meter), lessthan 0.1 S/m, less than 0.01 S/m, less than 0.001 S/m, less than 10⁻⁴S/m, less than 10⁻⁵ S/m, less than 10⁻⁶ S/m, less than 10⁻⁷ S/m, and/orwithin a range that includes or is bounded by any of the precedingexamples of average electrical conductivity. Upon heating, thesubsurface regions 32 may become more electrically conductive, achievingan average electrical conductivity of at least 10⁻⁵ S/m, at least 10⁻⁴S/m, at least 10⁻³ S/m, at least 0.01 S/m, at least 0.1 S/m, at least 1S/m, at least 10 S/m, at least 100 S/m, at least 1,000 S/m, and/orwithin a range that includes or is bounded by any of the precedingexamples of average electrical conductivity.

Where electrical conduction and/or resistive heating is not uniformwithin subsurface region 32, a subsurface shunt may form betweenelectrode assemblies 50 that serve the subsurface region 32. An exampleof such a subsurface shunt is schematically illustrated in FIG. 1 at 60.The subsurface shunt 60 may form because electrical conductivityincreases with increasing temperature and/or may form due toinhomogeneities (such as electrically-conductive and/orfluidically-conductive regions) within the subsurface region 32. Thesubsurface shunt 60 may be a region, a pathway, and/or a channel thatextends between two electrode assemblies 50 within the subsurface region32, and which has a higher electrical conductivity than the rest of thesubsurface region 32. Subsurface shunts 60 may be electrical shortsbetween electrode assemblies 50. Subsurface shunts 60 may divertelectrical current supplied by the electrode assemblies 50 away from thebulk of the subsurface regions 32 and into the subsurface shunts 60.Subsurface shunts 60 may be, and/or may include, a fluid path betweenelectrode assemblies 50. Subsurface shunts 60 may transmit fluidinjected into one electrode assembly 50 to another, connected, electrodeassembly 50.

When subsurface shunts 60 become sufficiently electrically conductive,the majority of electrical current passing between the electrodeassemblies 50 may travel through the subsurface shunts 60. The positivecorrelation between temperature and electrical conductivity mayreinforce and/or concentrate the subsurface shunts 60 as electricalcurrent flows through the subsurface shunts 60. Subsurface shunts 60 maybe very small as compared to the corresponding subsurface regions 32.The electrical current and the consequent heating may be very highlyconcentrated within the subsurface shunts 60.

The average electrical conductivity of subsurface shunts 60 may be atleast 10⁻⁵ S/m, at least 10⁻⁴ S/m, at least 10⁻³ S/m, at least 0.01 S/m,at least 0.1 S/m, at least 1 S/m, at least 10 S/m, at least 100 S/m, atleast 300 S/m, at least 1,000 S/m, at least 3,000 S/m, at least 10,000S/m, and/or within a range that includes or is bounded by any of thepreceding examples of average electrical conductivity. The electricalconductivity of the subsurface shunt 60 may be so great, relative to theremainder of the subsurface region 32, that the average electricalconductivity of the subsurface region 32 may be dominated by the averageelectrical conductivity of the included subsurface shunt 60.

The presence of a subsurface shunt 60 within the subsurface region 32may increase the electrical power flowing through the subsurface region32 and/or through the localized region corresponding to the subsurfaceshunt 60. The increased electrical power flowing through the subsurfaceshunt 60 may increase resistive heating within the subsurface shunt 60and/or may decrease electrical power flowing and/or resistive heatingoutside of the subsurface shunt 60. The presence of a subsurface shunt60 within the subsurface region 32 may be indicated by one or morethermal, mechanical, and/or electrical parameters (referred to as shuntindicators) relating to the bulk heating system 10, the subsurfaceregion 32, one or more of the electrode assemblies 50, and/or thesubsurface shunt 60 (at least the region of the subsurface region 32corresponding to the subsurface shunt). Shunt indicators may be thevalue of, and/or changes in, one or more thermal parameters, mechanicalparameters, electrical parameters, and/or related quantities. Thermalparameters may include the average temperature, a point (localized)temperature, a temperature difference, and/or a temperature gradient(temperature difference per length). Mechanical parameters may includefluid permeability and/or porosity. Electrical parameters may beelectrical conductivity-related parameters, which may include, and/ormay be, at least one of conductivity (a material's intrinsic ability toconduct electrical current), conductance (the ease with which electricalcurrent may flow through an object or defined region), resistivity (amaterial's intrinsic ability to oppose electrical current flow),resistance (the opposition to the flow of electrical current through anobject or defined region), current (electrical current flow), voltage(electrical potential), and/or a density and/or gradient of any of thepreceding examples of electrical conductivity-related parameters.

Electrical conductivity may be referred to as specific electricalconductance and/or volume conductivity. Electrical resistivity may bereferred to as specific electrical resistance and/or volume resistivity.Electrical conductivity, conductance, resistivity, and resistance eachmay be an AC and/or a DC quantity, i.e., each may be described as acomplex quantity, a magnitude, a phase angle, and/or afrequency-dependent quantity. When specifically referring to ACquantities, electrical conductivity may be called electrical admittivityand/or a real part of the complex electrical admittivity, electricalconductance may be called electrical admittance and/or a real part ofthe complex electrical admittance, electrical resistivity may be calledelectrical impeditivity and/or a real part of the complex electricalimpeditivity, and electrical resistance may be called electricalimpedance and/or a real part of the complex electrical impedance.

Bulk heating systems 10 may include a shunt mitigator 64 in and/or nearthe electrode assemblies 50, the subsurface region 32, and/or thesubsurface shunt 60. The shunt mitigator 64 may be a material configuredto selectively attenuate and/or eliminate electrical current flowthrough the subsurface shunt 60 in response to and/or in the presence ofthe subsurface shunt 60. The shunt mitigator 64 may be, optionallyselectively, located and/or placed in the electrode assemblies 50, thesubsurface region 32, and/or the subsurface shunt 60 to attenuate and/oreliminate electrical current flow through the subsurface shunt 60. Theshunt mitigator 64 may be, optionally selectively, located and/or placedbefore, during, and/or after the electrode assemblies 50 are formed. Theshunt mitigator 64 may be, optionally selectively, located and/or placedbefore, during, and/or after the subsurface shunt 60 is formed.

The shunt mitigator 64 may be a solid (e.g., particles, granules, etc.),a liquid, a gas, and/or a combination of solid, liquid, and/or gas. Theshunt mitigator 64 may be placed in (e.g., into porous regions within)the electrode assemblies 50, the subsurface region 32, and/or thesubsurface shunt 60 by flowing and/or injection under pressure. Wherethe shunt mitigator includes solids, the solids may be suspended and/ordispersed in a carrier fluid.

Shunt mitigator 64 may be within the electrode assemblies 50. Forexample, a solid and/or liquid shunt mitigator may be electricallyconductive and may be at least a portion of the electrical conductivematerial that forms an electrically conductive path from the surface 22to the subsurface region 32. Whether electrically conductive or not, thesolid and/or liquid shunt mitigator 64 may be flowed into the wellbore40 and/or the fracture 44 of the electrode assembly 50 with (other)electrically conductive materials (e.g., during formation of theelectrode assembly 50). When electrically conductive, the solid and/orliquid shunt mitigator 64 may be flowed into the wellbore 40 and/or thefracture 44 as the electrically conductive material of the electrodeassembly 50. The solid and/or liquid shunt mitigator 64 may be flowedinto electrode assembly 50 after the electrode assembly 50 alreadyincludes electrically conductive material.

Shunt mitigators 64 that are solid may be granular and may be at least aportion of the proppant that holds open a fracture 44 of the electrodeassembly. For example, shunt mitigator 64 may be flowed with, and/or as,proppant into a fracture 44 during formation and/or propping of thefracture 44.

As shunt mitigators 64 that are fluid (e.g., liquid and/or gaseous) maytend to not be retained within a selected location within the electrodeassemblies 50, the subsurface region 32, and/or the subsurface shunt 60,fluid shunt mitigators 64 may be flowed into at least one electrodeassembly 50 in anticipation of, during, and/or after formation of asubsurface shunt 60.

The shunt mitigator 64 may be configured to change one or moreproperties of the shunt mitigator in response to the presence of asubsurface shunt 60 (e.g., in response to a shunt indicator). The shuntmitigator 64 may be configured such that the change in its propertiesresults in a decrease in the electrical conductance (i.e., an increasein the electrical resistance) of the subsurface shunt 60 and/or adecrease in the electrical current flowing through the subsurface shunt60. The shunt mitigator 64 may be configured such that the change in itsproperties results in a decrease in the electrical conductivity (i.e.,an increase in the electrical resistivity) of the subsurface shunt 60and/or at least a portion of at least one of the electrode assemblies 50near the subsurface shunt 60. The properties may include at least one ofelectrical conductivity, electrical admittivity, electrical resistivity,electrical impeditivity, electric susceptibility, electric permittivity,magnetic susceptibility, magnetic permeability, density, viscosity,volume, and chemical activity.

The shunt mitigator 64 may be configured to decrease its electricalconductivity (i.e., to increase electrical resistivity) in response tothe shunt indicator. For example, the shunt mitigator 64 may decreaseits electrical conductivity in response to temperatures above apredetermined threshold. If electrically powered by a voltage-limitedpower source, an increase in temperature, which may be due to asubsurface shunt 60, may result in a decrease in electrical powerdissipated in the shunt mitigator 64 and consequently less heating dueto electricity flowing through the shunt mitigator 64. In response tothe shunt indicator, the shunt mitigator 64 may be configured todecrease its electrical conductivity at one or more frequencies, and/orabove or below a cutoff frequency.

The shunt mitigator 64 may be configured to chemically react, inresponse to the shunt indicator, with at least one of the subsurfaceregion 32, the subsurface shunt 60, and one or more of the electrodeassemblies 50. As an example, the shunt mitigator 64 may include, mayinclude a source of, and/or may be molecular oxygen, carbon dioxide, anoxidizing gas, and/or a gasification gas. These examples of shuntmitigators 64 may selectively react with (selectively oxidize)electrically-conductive carbon (e.g., residual char or a source ofelemental carbon) in the subsurface shunt 60, for example, because theshunt mitigator 64 is selectively placed in the subsurface shunt, and/orbecause electrically-conductive carbon is relatively more prevalent inthe subsurface shunt 60 than in the electrode assemblies 50. Agasification gas is a gas that, when added to electrically-conductivecarbon under appropriate conditions, reacts to form a gaseous carboncompound (such as carbon monoxide). A gasification gas may be carbondioxide or a gas that may be decomposed into a carbon dioxide product.When electrically-conductive carbon is oxidized, the amount ofelectrically-conductive carbon may be reduced and/or theelectrically-conductive carbon may be transformed into othercarbon-containing compounds that are less electrically-conductive (e.g.,carbon monoxide). Hence, oxidization of electrically-conductive carbonwithin and/or near the subsurface shunt 60 may reduce the electricalconductance, i.e., increase the electrical resistance, of the subsurfaceshunt 60.

The shunt mitigator 64 may be configured to decompose in response to theshunt indicator, to polymerize in response to the shunt indicator,and/or to melt in response to the shunt indicator. For example, theshunt mitigator 64 may include, and/or may be, a carbonate mineral suchas calcite and/or dolomite. Carbonate minerals may decompose at elevatedtemperatures that may be generated within the subsurface region 32and/or the subsurface shunt 60. For example, dolomite may decompose atabout 550° C., and calcite may decompose at about 700° C. Decompositionof carbonate minerals may result in the production of carbon dioxidegas, which may oxidize electrically conductive carbon in the subsurfaceshunt 60 and/or in a region near the subsurface shunt 60. As discussed,oxidization of electrically conductive carbon within and/or near thesubsurface shunt 60 may reduce the electrical conductance of thesubsurface shunt 60. The shunt mitigator 64 may be electricallyconductive and form at least a portion of the electrically conductivepath of an electrode assembly. When the shunt mitigator 64 decomposes,the shunt mitigator may become less electrically conductive and/or maytransform into a mobile material (e.g., a liquid and/or a gas) thatmigrates away from the site of decomposition. Such decomposition mayleave a void and/or a region of higher electrical resistance in theelectrical path to the subsurface shunt 60 and thereby reduce theelectrical conductance through the subsurface shunt 60.

The shunt mitigator 64 may be configured to change volume and/or densityin response to the shunt indicator. For example, the shunt mitigator 64may be electrically insulating and intermixed within the electricallyconductive material that forms the electrical path through an electrodeassembly to the subsurface region 32. When the subsurface shunt 60forms, the shunt mitigator 64 near the subsurface shunt 60 may expandand displace electrically conductive material near the subsurface shunt60 and thereby reduce the electrical conductance through the subsurfaceshunt 60.

The shunt mitigator 64 may be configured to undergo a state change inresponse to the presence of the subsurface shunt 60 (e.g., in responseto a shunt indicator). The state change is a change in property of theshunt mitigator 64. The shunt mitigator 64 may be configured such thatthe state change results in a decrease in the electrical conductance(i.e., an increase in the electrical resistance) of the subsurface shunt60 and/or a decrease in the electrical current flowing through thesubsurface shunt 60. The shunt mitigator 64 may be configured such thatthe state change results in a decrease in the electrical conductivity(i.e., an increase in the electrical resistivity) of the subsurfaceshunt 60 and/or at least a portion of at least one of the electrodeassemblies 50 near the subsurface shunt 60.

The state change may be an electromagnetic state change, anelectromagnetic phase transition, a paramagnetic transition, and/or aparaelectric transition. The state change may be a thermodynamic statechange, a thermodynamic phase transition, and/or a solid-liquidtransition. The state change may be a chemical state change, a chemicaldecomposition, and/or a polymerization. For example, the shunt mitigator64 may be configured to transition, in response to a shunt indicator, toa paramagnetic state, a paraelectric state, a liquid state, a decomposedstate, and/or a polymerized state.

The state change may be associated with a transition temperature of theshunt mitigator 64. The transition temperature may be a temperaturebetween the desired and/or expected temperature of the subsurface region32 (upon heating) and the temperature associated with an activesubsurface shunt 60. For example, the transition temperature may begreater than 200° C., greater than 300° C., greater than 400° C.,greater than 500° C., greater than 700° C., less than 1,200° C., lessthan 1,000° C., less than 900° C., less than 700° C., less than 500° C.,less than 400° C., less than 300° C., and/or within a range thatincludes or is bounded by any of the preceding examples of transitiontemperatures.

The transition temperature may be a Curie temperature, a paraelectrictransition temperature, a melting point, and/or a solidus temperature.The Curie temperature is the temperature above which a magnetic materialbecomes paramagnetic (loses its intrinsic magnetization). Theparaelectric transition temperature is the temperature above which adielectric material becomes paraelectric (loses its intrinsicpolarization). The magnetic and/or dielectric properties of a materialmay affect the electrical conductivity of the material when alternatingcurrent is applied. Shunt mitigators 64 that undergo a magnetic statetransition and/or a dielectric state transition (e.g., the transitiontemperature is a Curie temperature and/or a paraelectric transitiontemperature), may have reduced conductivity, may interrupt theelectrically conductive path to the subsurface shunt 60, and may reducethe electrical conductance through the subsurface shunt 60. Shuntmitigators 64 configured to undergo a magnetic state transition and/or adielectric state transition may include, and/or may be, a metal, a metalalloy, and/or a ceramic. For example, the shunt mitigator 64 mayinclude, and/or may be, a bismuth-manganese alloy and/or a strontiumtitanate compound.

The shunt mitigator 64 may be, and/or may include, a composite shuntmitigator 66. The composite shunt mitigator 66 may include at least twomaterials with different functional relationships between properties ofthe material and the shunt indicator (e.g., a thermal, mechanical,and/or electrical property). The materials of the composite shuntmitigator 66 may include one or more of the materials described withrespect to other types of shunt mitigators 64, and may include othermaterials. The composite shunt mitigator 66 may include a first materialwith a first functional relationship and a second material with a secondfunctional relationship. The property of the first functionalrelationship may be an electrical property such as electricalconductivity, electrical admittivity, electrical resistivity, electricalimpeditivity, electric susceptibility, electric permittivity, magneticsusceptibility, and/or magnetic permeability. The property of the secondfunctional relationship may be an electrical property, a physicalproperty, and/or a chemical property. For example, the property of thesecond functional relationship may be electrical conductivity,electrical admittivity, electrical resistivity, electrical impeditivity,electric susceptibility, electric permittivity, magnetic susceptibility,magnetic permeability, density, viscosity, volume, rigidity, and/orchemical activity. The combination of the functional relationships ofthe materials in a composite shunt mitigator 66 may be configured toproduce a composite functional relationship between one or moreproperties of the composite shunt mitigator 66 and the shunt indicator.The composite functional relationship may be a non-monotonic functionalrelationship, e.g., defining a mathematical extremum (maximum, minimum,inflection point, etc.) within the expected operating range of bulkheating system 10 and/or near the shunt indicator (e.g., at apredetermined value of a thermal, mechanical, and/or electrical propertyof the bulk heating system 10, the subsurface region 32, one or more ofthe electrode assemblies 50, and/or the subsurface shunt 60).

The shunt mitigator 64 may be configured to maintain a property of theshunt mitigator 64 in the presence of a subsurface shunt 60. The shuntmitigator 64 may be configured such that the placement and/or locationof the shunt mitigator 64 within and/or near the subsurface shunt 60results in a decrease in the electrical conductance (i.e., an increasein the electrical resistance) of the subsurface shunt 60 and/or adecrease in the electrical current flowing through the subsurface shunt60. The placement and/or location of the shunt mitigator 64 may resultin a decrease in the electrical conductivity (i.e., an increase in theelectrical resistivity) of the subsurface shunt 60 and/or at least aportion of at least one of the electrode assemblies 50 near thesubsurface shunt 60. The property of the shunt mitigator 64 may includeat least one of electrical conductivity, electrical admittivity,electrical resistivity, electrical impeditivity, electricsusceptibility, electric permittivity, magnetic susceptibility, magneticpermeability, density, viscosity, volume, and chemical activity.

For example, the shunt mitigator 64 may include, and/or may be, anelectrically insulating liquid, such as mineral oil, transformer oil,and/or a polymer. The electrically insulating liquid may be configuredto maintain its electrically insulating property in the presence of asubsurface shunt 60, e.g., at the temperature and/or electrical currentthat may be associated with the subsurface shunt 60. The electricallyinsulating liquid may not be present in the electrode assemblies 50and/or the subsurface region 32 before the formation of a subsurfaceshunt 60. Once the subsurface shunt 60 is formed and the presence of thesubsurface shunt 60 is detected, the electrically insulating liquid maybe injected into at least one of the electrode assemblies 50 and flowedto and/or into the subsurface shunt 60, thereby applying an electricallyinsulating mask to the subsurface shunt 60 and decreasing the electricalconductance through the subsurface shunt 60.

Subsurface shunts 60 may be mitigated during bulk heating of subsurfaceformations 20 by performing bulk heating methods 100. In the example ofFIG. 2, bulk heating methods 100 may include electrically powering 110at least a pair of electrode assemblies (such as electrode assemblies50) that are within a subsurface formation (such as subsurface formation20), to resistively heat at least a subsurface region (such assubsurface region 32 and/or in situ resistive heater 34) between thepair of electrode assemblies with electrical current flowing through thesubsurface region between the pair of electrode assemblies. The bulkheating methods 100 may include flowing 112 shunt mitigator (such asshunt mitigator 64) into at least one of the electrode assemblies.Responsive to a shunt indicator that indicates the presence and/orformation of a subsurface shunt (such as subsurface shunt 60) betweenthe pair of electrode assemblies, the bulk heating methods 100 mayinclude mitigating 114 the subsurface shunt with the shunt mitigator.

Electrically powering 110 may include applying a voltage across and/orsupplying an electrical current through the pair of electrodeassemblies. Electrically powering 110 may include supplying an ACcurrent (i.e., an alternating current) to the pair of electrodeassemblies. Electrically powering 110 may include electrically poweringthe pair of electrode assemblies while at least one of the electrodeassemblies includes the shunt mitigator. For example, electricallypowering 110 may include electrically powering the electrode assemblyconfiguration of FIG. 1, where shunt mitigator 64 may be present in oneor both of the electrode assemblies 50 and/or in the subsurface region32 between the electrode assemblies 50.

Electrically powering 110 may include heating the subsurface region topyrolyze organic matter in the subsurface formation, to pyrolyze organicmatter to create hydrocarbon fluids, and/or to mobilize hydrocarbonfluids within the subsurface formation. Electrically powering 110 mayinclude heating the subsurface region to an average temperature and/or apoint (localized) temperature of at least 150° C., at least 250° C., atleast 350° C., at least 450° C., at least 550° C., at least 700° C., atleast 800° C., at least 900° C., at most 1000° C., at most 900° C., atmost 800° C., at most 700° C., at most 550° C., at most 450° C., at most350° C., at most 270° C., and/or within a range that includes or isbounded by any of the preceding examples of temperature.

Electrically powering 110 to resistively heat the subsurface region mayinclude forming an electrical circuit between the electrode assembliesand the subsurface region. Electrically powering 110 may includeelectrically powering the subsurface region to form an in situ resistiveheater (such as in situ resistive heater 34) between the electrodeassemblies.

Electrically powering 110 may begin without a subsurface shunt beingpresent between the electrode assemblies. Electrically powering 110 mayresult in a subsurface shunt forming between the electrode assemblieswithin the subsurface region (and/or within the in situ resistiveheater).

Bulk heating methods 100 of FIG. 2 may include flowing 112 the shuntmitigator into at least one of the electrode assemblies. Flowing 112 maybe performed before, during, and/or after electrically powering 110and/or before, during, and/or after the formation of the subsurfaceshunt.

Flowing 112 may include injecting a slurry and/or a fluid that includes,and/or is, the shunt mitigator into at least one of the electrodeassemblies. Flowing 112 may include flowing shunt mitigator into thesubsurface region, the in situ resistive heater, and/or the subsurfaceshunt. Flowing 112 may include applying a pressure differential betweenthe pair of electrode assemblies (e.g., injecting into one electrodeassembly while drawing a hydrostatic pressure on the other electrodeassembly). As shown in FIG. 1, flowing 112 may result in a bulk heatingsystem 10 with shunt mitigator 64 within the electrode assemblies 50,the subsurface region 32, the in situ resistive heater 34, and/or thesubsurface shunt 60 (if present). Flowing 112 may result in shuntmitigator 64 selectively located near and/or within the subsurface shunt60.

Flowing 112 may be performed before, during, and/or after determining116 the presence of the subsurface shunt between the electrodeassemblies. Determining 116 may include measuring an electricalconductivity-related parameter between the pair of electrode assemblies.The electrical conductivity-related parameter may include, and/or maybe, conductivity, conductance, resistivity, resistance, admittivity,admittance, impeditivity, impedance, current, voltage, a pointtemperature and/or an average temperature. Determining 116 may includemeasuring a fluid permeability-related parameter between the pair ofelectrode assemblies.

For example, determining 116 may include determining that the averageelectrical conductivity of the subsurface shunt is at least 10⁻⁵ S/m, atleast 10⁻⁴ S/m, at least 10⁻³ S/m, at least 0.01 S/m, at least 0.1 S/m,at least 1 S/m, at least 10 S/m, at least 100 S/m, at least 300 S/m, atleast 1,000 S/m, at least 3,000 S/m, at least 10,000 S/m, and/or withina range that includes or is bounded by any of the preceding examples ofaverage electrical conductivity. Determining 116 may include determiningthat the average electrical conductivity of the subsurface region is atleast 10⁻⁵ S/m, at least 10⁻⁴ S/m, at least 10⁻³ S/m, at least 0.01 S/m,at least 0.1 S/m, at least 1 S/m, at least 10 S/m, at least 100 S/m,and/or within a range that includes or is bounded by any of thepreceding examples of average electrical conductivity.

Bulk heating methods 100 of FIG. 2 may include mitigating 114,responsive to the shunt indicator, the subsurface shunt between the pairof electrode assemblies with the shunt mitigator. Prior to mitigating114, and as shown in FIG. 3, the subsurface shunt 60 has formed (or hasbegun to form) and shunt mitigator 64 may be present near and/or withinthe subsurface shunt 60. As discussed, the shunt mitigator 64 may belocated near and/or within the subsurface shunt 60 by flowing 112 theshunt mitigator into at least one of the electrode assemblies 50. Theshunt mitigator 64 may be present prior to the formation of thesubsurface shunt 60 and/or may be located near and/or within thesubsurface shunt 60 after the formation of the subsurface shunt 60.

Once the shunt mitigator 64 is present near and/or within the subsurfaceshunt 60 and the subsurface shunt 60 exhibits a shunt indicator (e.g., athermal, mechanical, and/or electrical parameter value and/or change invalue), the shunt mitigator 64 may selectively attenuate and/oreliminate electrical current (and/or the possibility of electricalcurrent transmission) through the subsurface shunt 60. The shuntmitigator 64 may selectively attenuate and/or eliminate electricalcurrent (and/or the possibility of electrical current transmission)through the subsurface shunt 60 by being selectively located near and/orwithin the subsurface shunt 60 and/or by changing a property in responseto the shunt indicator.

Returning to FIG. 2, mitigating 114 may be performed before, during,and/or after determining 116 the presence of the subsurface shuntbetween the electrode assemblies. Upon determining 116 the presence ofthe subsurface shunt, mitigating 114 may prompt flowing 112 the shuntmitigator to mitigate the subsurface shunt.

Mitigating 114 may include decreasing the electrical conductance (i.e.,increasing the electrical resistance) of the subsurface shunt.Mitigating 114 may include electrically isolating the subsurface shuntfrom one or more of the electrode assemblies.

Mitigating 114 may include forming a modified subsurface region, asillustrated in FIG. 4. Mitigating 114 may include forming a mitigatedsubsurface shunt 62 from the subsurface shunt 60 and thereby forming amodified in situ resistive heater 36, which includes the mitigatedsubsurface shunt 62, from the in situ resistive heater 34.

After mitigating 114, the electrode assemblies may have reducedelectrical conductivity. Bulk heating methods 100 may include, after themitigating 114, introducing electrically conductive material into atleast one of the electrode assemblies. Electrically conductive materialmay include granular material, granules, particles, filaments, metal,granular metal, metal coated particles, coke, graphite, electricallyconductive gel, and/or electrically conductive liquid.

Bulk heating methods 100 may include electrically powering the pair ofelectrode assemblies 50 to resistively heat the modified in situresistive heater 36 with electrical current flowing through the modifiedin situ resistive heater between the pair of electrode assemblies 50.

Bulk heating methods 100 may include monitoring the bulk heating system10 for shunt indicators. For example, bulk heating methods 100 mayinclude measuring one or more electrical conductivity-related parametersand/or fluid permeability-related parameters between the pair ofelectrode assemblies.

FIG. 5 schematically represents an example of bulk heating methods 100which may or may not utilize a shunt mitigator. Bulk heating methods 100of FIG. 5 may include electrically powering 110 the pair of electrodeassemblies to resistively heat an in situ resistive heater between thepair of electrodes. The bulk heating methods 100 may include determining116 the presence of the subsurface shunt between the pair of electrodeassemblies. Determining 116 may be similar and/or identical to thedetermining described above with respect to FIG. 2. Upon determining116, the bulk heating methods 100 may include mitigating 114 thesubsurface shunt to form a modified in situ resistive heater. The bulkheating methods 100 may include electrically powering 118 the pair ofelectrode assemblies to resistively heat the modified in situ resistiveheater. Electrically powering 118 may be similar and/or identical to theelectrically powering described above with respect to FIG. 2.

Though mitigating 114 of the example of FIG. 5 may include aspects orfeatures described with respect to the example of FIG. 2, mitigating 114may include methods of mitigation that do not utilize a shunt mitigator.Mitigating 114 may include thermal-electrical ablation of at least aportion of the subsurface shunt. Thermal-electric ablation may includeapplying a relatively large impulse of electrical power to thesubsurface shunt, by applying such impulse to the pair of electrodeassemblies. The impulse of electrical power may be configured toselectively heat the subsurface shunt and/or at least a portion of theelectrode assemblies near the subsurface shunt due to the electricalconductivity of the subsurface shunt. The heating due to the impulse ofelectrical power may thermally-electrically ablate at least a portion ofthe subsurface shunt, or at least a portion of one of the electrodeassemblies near the subsurface shunt, much like blowing a fuse. Afterthe thermal-electric ablation, the subsurface shunt may be electricallyisolated from at least one of the electrode assemblies and/or mayinclude an electrical discontinuity. The impulse of electrical power maybe at least 1,000 V, at least 10,000 V, and/or at least 100,000 V. Theimpulse of electrical power may be applied for less than 10 seconds,less than 1 second, less than 0.1 seconds, and/or less than 0.01seconds. In the example of FIG. 2, mitigating 114 may includethermally-electrically ablating as described.

Bulk heating methods 100 may include producing hydrocarbon fluids fromthe subsurface formation. The hydrocarbon fluids may be produced to thesurface via a production well in the subsurface formation. Theproduction well may be proximate to one or more of the electrodeassemblies. The production well may be in fluid communication with oneor more subsurface regions.

Additionally or alternately, the present invention can be describedaccording to one or more of the following embodiments.

Embodiment 1. A method for bulk heating a subsurface formation with atleast a pair of electrode assemblies in the subsurface formation, themethod comprising:

electrically powering the pair of electrode assemblies to resistivelyheat a subsurface region between the pair of electrode assemblies withelectrical current flowing through the subsurface region between thepair of electrode assemblies;

flowing a shunt mitigator into at least one of the pair of electrodeassemblies; and

responsive to a shunt indicator, mitigating a subsurface shunt betweenthe pair of electrode assemblies with the shunt mitigator, wherein theshunt indicator indicates a presence of the subsurface shunt.

Embodiment 2. The method of embodiment 1, wherein the flowing occursafter determining the presence of the subsurface shunt.

Embodiment 3. The method of embodiment 2, wherein the determiningcomprises measuring between the pair of electrode assemblies at leastone of an electrical conductivity-related parameter, a thermalparameter, and a fluid permeability-related parameter.

Embodiment 4. The method of any of embodiments 2-3, wherein thedetermining comprises determining that an average electricalconductivity of the subsurface region is at least 0.01 S/m.

Embodiment 5. The method of any of embodiments 1-4, wherein the flowingoccurs one of before, during and after the electrically powering.

Embodiment 6. The method of any of embodiments 1-5, wherein the shuntindicator is at least one of a temperature difference in the subsurfaceregion, a temperature gradient in the subsurface region, a currentdensity in the subsurface region, a current gradient in the subsurfaceregion, a current density in the subsurface shunt, an electricalconductivity of the subsurface shunt, an electrical admittivity of thesubsurface shunt, an electrical resistivity of the subsurface shunt, anelectrical impeditivity of the subsurface shunt, a point temperature ofat least one electrode assembly, a point temperature near the subsurfaceshunt, and an average temperature of the subsurface shunt.

Embodiment 7. The method of any of embodiments 1-6, wherein the shuntmitigator is selected to change a property in response to the shuntindicator.

Embodiment 8. The method of embodiment 7, wherein the mitigatingcomprises mitigating the subsurface shunt with the change of theproperty of the shunt mitigator.

Embodiment 9. The method of any of embodiments 7-8, wherein the shuntmitigator is configured to decrease the electrical current flowingthrough the subsurface shunt by changing the property in response to theshunt indicator.

Embodiment 10. The method of any of embodiments 7-9, wherein theproperty is at least one of electrical conductivity, electricaladmittivity, electrical resistivity, electrical impeditivity, electricsusceptibility, electric permittivity, magnetic susceptibility, magneticpermeability, density, viscosity, volume, and chemical activity.

Embodiment 11. The method of any of embodiments 1-10, wherein the shuntmitigator is configured to one of decrease and increase the electricalconductance of the subsurface shunt.

Embodiment 12. The method of any of embodiments 1-11, wherein the shuntmitigator is configured to decrease the electrical conductivity of atleast a portion of the one of the pair of electrode assemblies near thesubsurface shunt.

Embodiment 13. The method of any of embodiments 1-12, wherein the shuntmitigator is configured to increase the electrical resistivity of atleast a portion of the one of the pair of electrode assemblies near thesubsurface shunt.

Embodiment 14. The method of any of embodiments 1-13, wherein the shuntmitigator is selected to at least one of decompose in response to theshunt indicator, polymerize in response to the shunt indicator, and meltin response to the shunt indicator.

Embodiment 15. The method of any of embodiments 1-14, wherein the shuntmitigator is selected to chemically react, in response to the shuntindicator, with at least one of the one of the pair of electrodeassemblies, the subsurface region, and the subsurface shunt.

Embodiment 16. The method of any of embodiments 1-15, wherein the shuntmitigator is selected to undergo a state change in response to the shuntindicator.

Embodiment 17. The method of embodiment 16, wherein the shunt indicatorundergoes a state change, and the state change is at least one of anelectromagnetic state change, an electromagnetic phase transition, aparamagnetic transition, and a paraelectric transition.

Embodiment 18. The method of any of embodiments 16-17, wherein the statechange is at least one of a thermodynamic state change, a thermodynamicphase transition, and a solid-liquid transition.

Embodiment 19. The method of any of embodiments 16-18, wherein the statechange is at least one of a chemical state change, a chemicaldecomposition, and a polymerization.

Embodiment 20. The method of any of embodiments 16-19, wherein the shuntmitigator is selected to transition, in response to the shunt indicator,to at least one of a paramagnetic state and a paraelectric state.

Embodiment 21. The method of any of embodiments 16-20, wherein the shuntmitigator is selected to transition, in response to the shunt indicator,to a liquid state.

Embodiment 22. The method of any of embodiments 16-21, wherein the shuntmitigator is selected to transition, in response to the shunt indicator,to at least one of a decomposed state and a polymerized state.

Embodiment 23. The method of any of embodiments 16-22, wherein the statechange is associated with a transition temperature of the shuntmitigator.

Embodiment 24. The method of embodiment 23, wherein the transitiontemperature is greater than 500° C.

Embodiment 25. The method of any of embodiments 23-24, wherein thetransition temperature is at least one of a Curie temperature, aparaelectric transition temperature, a melting point, and a solidustemperature.

Embodiment 26. The method of any of embodiments 1-25, wherein the shuntmitigator includes a composite shunt mitigator, wherein the compositeshunt mitigator includes a first material that defines a firstfunctional relationship between an electrical property of the firstmaterial and the shunt indicator, and wherein the composite shuntmitigator includes a second material that defines a second functionalrelationship between a property of the second material and the shuntindicator.

Embodiment 27. The method of embodiment 26, wherein the electricalproperty of the first material includes at least one of electricalconductivity, electrical admittivity, electrical resistivity, electricalimpeditivity, electric susceptibility, electric permittivity, magneticsusceptibility, and magnetic permeability.

Embodiment 28. The method of any of embodiments 26-27, wherein theproperty of the second material includes at least one of electricalconductivity, electrical admittivity, electrical resistivity, electricalimpeditivity, electric susceptibility, electric permittivity, magneticsusceptibility, magnetic permeability, density, viscosity, volume,rigidity, and chemical activity.

Embodiment 29. The method of any of embodiments 1-28, wherein at leastone of the pair of electrode assemblies includes a fracture.

Embodiment 30. The method of embodiment 29, wherein the fracturecomprises proppant that includes at least one of electrically conductivematerial and electrically conductive granular material.

Embodiment 31. The method of any of embodiments 29-30, wherein thefracture is one of substantially vertical and substantially horizontal.

Embodiment 32. The method of any of embodiments 29-31, wherein the pairof electrode assemblies includes a first electrode assembly and a secondelectrode assembly, wherein the first electrode assembly includes afirst fracture, the second electrode assembly includes a secondfracture, and wherein the first fracture and the second fracture aresubstantially parallel.

Embodiment 33. The method of any of embodiments 1-32, wherein eachelectrode assembly of the pair of electrode assemblies includes anelectrically conductive material that includes at least one of granularmaterial, granules, particles, filaments, metal, granular metal, metalcoated particles, coke, graphite, electrically conductive gel, andelectrically conductive liquid.

Embodiment 34. The method of any of embodiments 1-33, wherein theelectrically powering includes electrically powering the pair ofelectrode assemblies while at least the one of the pair of electrodeassemblies includes the shunt mitigator.

Embodiment 35. The method of any of embodiments 1-34, wherein themitigating includes forming a mitigated subsurface shunt from thesubsurface shunt and thereby forming a modified subsurface region withthe mitigated subsurface shunt from the subsurface region, and whereinthe method further comprises electrically powering the pair of electrodeassemblies to resistively heat the modified subsurface region withelectrical current flowing through the modified subsurface regionbetween the pair of electrode assemblies.

Embodiment 36. The method of any of embodiments 1-35, wherein theelectrically powering includes heating the subsurface region to anaverage temperature of at least 250° C.

Embodiment 37. The method of any of embodiments 1-36, wherein theelectrically powering includes heating organic matter in the subsurfaceformation to generate mobile hydrocarbon fluids.

Embodiment 38. The method of any of embodiments 1-37, further comprisingproducing hydrocarbon fluids from the subsurface formation.

Embodiment 39. A method for bulk heating a subsurface formation with atleast a pair of electrode assemblies in the subsurface formation, themethod comprising:

electrically powering the pair of electrode assemblies to resistivelyheat an in situ resistive heater, wherein the in situ resistive heateris a subsurface region of the subsurface formation between the pair ofelectrode assemblies;

upon determining a presence of a subsurface shunt between the pair ofelectrode assemblies, forming a modified in situ resistive heater bymitigating the subsurface shunt; and electrically powering the pair ofelectrode assemblies to resistively heat the modified in situ resistiveheater.

Embodiment 40. The method of embodiment 39, wherein the mitigatingincludes decreasing the electrical conductance of the subsurface shunt.

Embodiment 41. The method of any of embodiments 39-40, wherein themitigating includes increasing the electrical resistance of thesubsurface shunt.

Embodiment 42. The method of any of embodiments 39-41, wherein themitigating includes electrically isolating the subsurface shunt from atleast one of the pair of electrode assemblies.

Embodiment 43. The method of any of embodiments 39-42, wherein themitigating includes mitigating the subsurface shunt with a shuntmitigator.

Embodiment 44. The method of embodiment 43, wherein the mitigatingincludes flowing the shunt mitigator into at least one of the pair ofelectrode assemblies.

Embodiment 45. The method of any of embodiments 43-44, wherein the shuntmitigator is configured to decrease the electrical conductance of thesubsurface shunt.

Embodiment 46. The method of any of embodiments 43-45, wherein the shuntmitigator is configured to increase the electrical resistance of thesubsurface shunt.

Embodiment 47. The method of any of embodiments 43-46, wherein the shuntmitigator is configured to decrease the electrical conductivity of atleast a portion of an electrode assembly of the pair of electrodeassemblies near the subsurface shunt.

Embodiment 48. The method of any of embodiments 43-47, wherein the shuntmitigator is configured to increase the electrical resistivity of atleast a portion of an electrode assembly of the pair of electrodeassemblies near the subsurface shunt.

Embodiment 49. The method of any of embodiments 43-48, wherein the shuntmitigator is selected to chemically react with at least one of anelectrode assembly of the pair of electrode assemblies and thesubsurface shunt.

Embodiment 50. The method of any of embodiments 39-49, wherein themitigating includes injecting a fluid to chemically alter an electricalproperty of the subsurface shunt.

Embodiment 51. The method of embodiment 50, wherein the fluid includesat least one of molecular oxygen, carbon dioxide, an oxidizing gas, anda gasification gas.

Embodiment 52. The method of any of embodiments 39-51, wherein themitigating includes injecting an electrically insulating liquid into thesubsurface shunt.

Embodiment 53. The method of any of embodiments 39-52, wherein themitigating includes thermally-electrically ablating at least a portionof the subsurface shunt.

Embodiment 54. The method of any of embodiments 39-53, furthercomprising, after the mitigating, introducing electrically conductivematerial into at least one of the pair of electrode assemblies.

Embodiment 55. A subsurface formation, comprising:

at least a pair of electrode assemblies;

wherein each electrode assembly of the pair of electrode assembliesincludes an electrically conductive material; and

wherein at least one electrode assembly of the pair of electrodeassemblies includes a shunt mitigator that is selected to undergo astate change in response to a shunt indicator.

Embodiment 56. The subsurface formation of embodiment 55, wherein theshunt indicator indicates a presence of a subsurface shunt between thepair of electrode assemblies.

Embodiment 57. The subsurface formation of any of embodiments 55-56,wherein the shunt indicator is at least one of a temperature differencein the subsurface region, a temperature gradient in the subsurfaceregion, a current density in the subsurface region, a current gradientin the subsurface region, a current density in the subsurface shunt, anelectrical conductivity of the subsurface shunt, an electricaladmittivity of the subsurface shunt, an electrical resistivity of thesubsurface shunt, an electrical impeditivity of the subsurface shunt, apoint temperature of at least one electrode assembly, a pointtemperature near the subsurface shunt, and an average temperature of thesubsurface shunt.

Embodiment 58. The subsurface formation of any of embodiments 55-57,wherein the shunt mitigator undergoes a state change, and the statechange is at least one of an electromagnetic state change, anelectromagnetic phase transition, a paramagnetic transition, and aparaelectric transition.

Embodiment 59. The subsurface formation of any of embodiments 55-58,wherein the state change is at least one of a thermodynamic statechange, a thermodynamic phase transition, and a solid-liquid transition.

Embodiment 60. The subsurface formation of any of embodiments 55-59,wherein the state change is at least one of a chemical state change, achemical decomposition, and a polymerization.

Embodiment 61. The subsurface formation of any of embodiments 55-60,wherein the shunt mitigator is selected to transition, in response tothe shunt indicator, to at least one of a paramagnetic state and aparaelectric state.

Embodiment 62. The subsurface formation of any of embodiments 55-61,wherein the shunt mitigator is selected to transition, in response tothe shunt indicator, to a liquid state.

Embodiment 63. The subsurface formation of any of embodiments 55-62,wherein the shunt mitigator is selected to transition, in response tothe shunt indicator, to at least one of a decomposed state and apolymerized state.

Embodiment 64. The subsurface formation of any of embodiments 55-63,wherein the state change is associated with a transition temperature ofthe shunt mitigator.

Embodiment 65. The subsurface formation of embodiment 64, wherein thetransition temperature is greater than 500° C.

Embodiment 66. The subsurface formation of any of embodiments 64-65,wherein the transition temperature is at least one of a Curietemperature, a paraelectric transition temperature, a melting point, anda solidus temperature.

The various disclosed elements of systems and steps of methods disclosedherein are not required of all systems and methods according to thepresent disclosure, and the present disclosure includes all novel andnon-obvious combinations and subcombinations of the various elements andsteps disclosed herein. Moreover, one or more of the various elementsand steps disclosed herein may define independent inventive subjectmatter that is separate and apart from the whole of a disclosedapparatus or method. Accordingly, such inventive subject matter is notrequired to be associated with the specific systems and methods that areexpressly disclosed herein, and such inventive subject matter may findutility in systems and/or methods that are not expressly disclosedherein.

In the present disclosure, several examples have been discussed and/orpresented in the context of flow diagrams, or flow charts, in which themethods are shown and described as a series of blocks, or steps. Unlessspecifically set forth in the accompanying description, the order of theblocks may vary from the illustrated order in the flow diagram,including with two or more of the blocks (or steps) occurring in adifferent order and/or concurrently.

INDUSTRIAL APPLICABILITY

The systems and methods of the present disclosure are applicable to theoil and gas industry.

It is believed that the following claims particularly point out certaincombinations and subcombinations that are novel and non-obvious. Othercombinations and subcombinations of features, functions, elements and/orproperties may be claimed through amendment of the present claims orpresentation of new claims in this or a related application. Suchamended or new claims, whether different, broader, narrower, or equal inscope to the original claims, are also regarded as included within thesubject matter of the present disclosure.

1. A method for bulk heating a subsurface formation with at least a pairof electrode assemblies in the subsurface formation, the methodcomprising: electrically powering the pair of electrode assemblies toresistively heat a subsurface region between the pair of electrodeassemblies with electrical current flowing through the subsurface regionbetween the pair of electrode assemblies; flowing a shunt mitigator intoat least one of the pair of electrode assemblies; and responsive to ashunt indicator, mitigating a subsurface shunt between the pair ofelectrode assemblies with the shunt mitigator, wherein the shuntindicator indicates a presence of the subsurface shunt.
 2. The method ofclaim 1, wherein the flowing occurs after determining the presence ofthe subsurface shunt.
 3. The method of claim 2, wherein the determiningcomprises measuring between the pair of electrode assemblies at leastone of an electrical conductivity-related parameter, a thermalparameter, and a fluid permeability-related parameter.
 4. The method ofclaim 2, wherein the determining comprises determining that an averageelectrical conductivity of the subsurface region is at least 0.01 S/m.5. The method of claim 2, wherein the shunt mitigator is configured toincrease the electrical resistivity of at least a portion of the pair ofelectrode assemblies near the subsurface shunt.
 6. The method of claim5, wherein the shunt mitigator is selected to at least one of decomposein response to the shunt indicator, polymerize in response to the shuntindicator, and melt in response to the shunt indicator.
 7. The method ofclaim 5, wherein the shunt mitigator is selected to chemically react, inresponse to the shunt indicator, with at least one of the pair ofelectrode assemblies, the subsurface region, and the subsurface shunt.8. The method of claim 5, wherein the shunt mitigator is selected toundergo a state change in response to the shunt indicator.
 9. The methodof claim 8, wherein the shunt mitigator undergoes a state change, andthe state change is at least one of an electromagnetic state change, anelectromagnetic phase transition, a paramagnetic transition, and aparaelectric transition.
 10. The method of claim 2, wherein the shuntmitigator includes a composite shunt mitigator, wherein the compositeshunt mitigator includes a first material that defines a firstfunctional relationship between an electrical property of the firstmaterial and the shunt indicator, and wherein the composite shuntmitigator includes a second material that defines a second functionalrelationship between a property of the second material and the shuntindicator.
 11. The method of claim 10, wherein the electrical propertyof the first material includes at least one of electrical conductivity,electrical admittivity, electrical resistivity, electrical impeditivity,electric susceptibility, electric permittivity, magnetic susceptibility,and magnetic permeability.
 12. The method of claim 10, wherein theproperty of the second material includes at least one of electricalconductivity, electrical admittivity, electrical resistivity, electricalimpeditivity, electric susceptibility, electric permittivity, magneticsusceptibility, magnetic permeability, density, viscosity, volume,rigidity, and chemical activity.
 13. A method for bulk heating asubsurface formation with at least a pair of electrode assemblies in thesubsurface formation, the method comprising: electrically powering thepair of electrode assemblies to resistively heat an in situ resistiveheater, wherein the in situ resistive heater is a subsurface region ofthe subsurface formation between the pair of electrode assemblies; upondetermining a presence of a subsurface shunt between the pair ofelectrode assemblies, forming a modified in situ resistive heater bymitigating the subsurface shunt; and electrically powering the pair ofelectrode assemblies to resistively heat the modified in situ resistiveheater.
 14. The method of claim 13, wherein the mitigating includesinjecting a fluid to chemically alter an electrical property of thesubsurface shunt.
 15. The method of claim 14, wherein the fluid includesat least one of molecular oxygen, carbon dioxide, an oxidizing gas, anda gasification gas.
 16. The method of claim 13, wherein the mitigatingincludes injecting an electrically insulating liquid into the subsurfaceshunt.
 17. A subsurface formation, comprising: at least a pair ofelectrode assemblies; wherein each electrode assembly of the pair ofelectrode assemblies includes an electrically conductive material; andwherein at least one electrode assembly of the pair of electrodeassemblies includes a shunt mitigator that is selected to undergo astate change in response to a shunt indicator.
 18. The subsurfaceformation of claim 17, wherein the shunt indicator indicates a presenceof a subsurface shunt between the pair of electrode assemblies.
 19. Thesubsurface formation of claim 17, wherein the shunt indicator is atleast one of a temperature difference in the subsurface region, atemperature gradient in the subsurface region, a current density in thesubsurface region, a current gradient in the subsurface region, acurrent density in the subsurface shunt, an electrical conductivity ofthe subsurface shunt, an electrical admittivity of the subsurface shunt,an electrical resistivity of the subsurface shunt, an electricalimpeditivity of the subsurface shunt, a point temperature of at leastone electrode assembly, a point temperature near the subsurface shunt,and an average temperature of the subsurface shunt.
 20. The subsurfaceformation of claim 17, wherein the shunt mitigator undergoes a statechange, and the state change is at least one of an electromagnetic statechange, an electromagnetic phase transition, a paramagnetic transition,and a paraelectric transition.